I am planning to upgrade my CS4 to CS5.5 (Design Premium) - I heard Lightroom 3 has new cool features such as new and improved noise-reduction in photos. Do you get pretty much all the features of Adobe Lightroom 3 in Photoshop CS5.5? I just want to know if it is necessary to buy Lightroom 3 at any point for any reason. Thanks,
Lightroom and Photoshop aren't really (supposed to be) competing products -- they're complementary products that overlap. Lightroom is all about managing your workflow, which just happens to include image processing in most cases. Photoshop, on the other hand, is image processing to the max, but it doesn't really do much to help your workflow. There's very little you can do in Lightroom that you can't do in Photoshop, therefore, but if you're working on a lot of photos, you'll probably find that Lightroom saves you quite a bit of time.
The most common workflow for both of these products together uses Lightroom to import photos, then tag and cull them for further processing (or vice versa). A fair bit of general image processing can be done right in Lightroom, but for images that you really want to spend some time on, you can shoot those photos over to Photoshop for heavy-duty processing and (optionally) pull the results back into Lightroom.
For areas where these products overlap (RAW processing, etc.), they're generally either equivalent or in some cases actually use the same binary bits, so if you don't think you need the workflow portions of Lightroom, you shouldn't miss out on any of its image processing features. For what it's worth, people who value the workflow stuff in Lightroom but don't need to tap all the power of Photoshop can often get by with Lightroom plus Photoshop Elements -- that's a great combo, too.
Being a recent convert to Lightroom, I can say the big benefit is the organization and workflow capability versus PS+Bridge. That combination does work, granted - I used it for quite some time. But Lightroom is a whole other animal. Tagging, rating, and meta edits seem much smoother in Lightroom.
In common is the Camera Raw capability - you're not missing out on that either way. Photoshop is an all-round image editor, but not focused on photo workflow. The way I work is to use Lightroom for post-processing tasks such as tagging and such, and only switch to Photoshop if there's serious image editing or compositing to do e.g. panoramas.
In terms of RAW conversion, both Photoshop and Lightroom use Adobe Camera Raw. You won't be missing functionality, although it is exposed via a different UI in Lightroom than in Photoshop's Camera RAW dialog.
Many people who shoot a lot use Lightroom for almost all post-processing, diving into Photoshop only when some significant image restructuring needs to be undertaken at the pixel level.
But the direct answer to your question is no. And the additional answer is that Adobe Bridge (included with PS) should handle a good number of tasks one might use Lightroom for (editing, metatagging, etc.). You just won't be able to do a global search of your entire image library using metadata.